Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E03: Novel Transport in Topological Systems |
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Sponsoring Units: DCMP Chair: Linda Ye, Massachusetts Institute of Technology Room: BCEC 107B |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E03.00001: Ultrafast Photocurrents in the Weyl Semimetal TaAs Nicholas Sirica, Ra'anan Tobey, Lingxiao Zhao, Genfu Chen, Bing Xu, Run Yang, Bing Shen, Dzmitry A. Yarotski, Pamela Bowlan, Stuart Trugman, Jian-Xin Zhu, Yaomin Dai, Abul K Azad, Ni Ni, Xianggang Qiu, Antoinette Taylor, Rohit P Prasankumar We investigate polarization-dependent, ultrafast photocurrents in the Weyl semimetal TaAs using terahertz (THz) emission spectroscopy. Our results reveal that highly directional, transient photocurrents are generated along the non-centrosymmetric c-axis regardless of incident light polarization, while helicity-dependent photocurrents are excited within the ab-plane. This is consistent with both the bulk photovoltaic effect and the circular photogalvanic effect observed in direct photocurrent experiments, and provides additional insight into their microscopic origin by way of the dynamical information gained from the emitted THz waveform. |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E03.00002: Elastic gauge fields and zero-field 3D quantum Hall effect in hyperhoneycomb lattices Sang Wook Kim, Bruno Uchoa We derive the elastic gauge fields that emerge from lattice deformations in the hyperhoneycomb lattice, a three-dimensional structure with trigonally connected sites. In its semimetallic form, this lattice is a nodal-line semimetal with a closed loop of Dirac nodes. Using strain engineering, we find the strain fields that create nearly uniform 3D Landau level quantization. In the 3D quantum anomalous Hall phase, we show that the elastic Hall viscosity is ηH=β2√3/(16πa3), where a is the lattice constant. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E03.00003: Proximal Anomalous Hall Effect in Ferromagnetic Insulator/Bulk-insulating BiSbTeSe2 Heterostructures Shihua Zhao, Haiming Deng, Daniel Rhodes, James Hone, Marcin Konczykowski, Agnieszka Wolos, Lia Krusin-Elbaum Realization of Quantized Anomalous Hall Effect in topological insulators (TIs) thus far has been limited to ultra-thin MBE films of Cr- or V-doped (Bi,Sb)2Te3. In this system the disorder of the dopant landscape may limit the quantization temperature range in which the chiral channels can be observed. The alternative is to obtain proximal ferromagnetism in a 3D TI by creating a trilayer sandwich comprising ferromagnetic insulator (FMI) on the top and bottom surfaces of a TI. Here we report on the trilayer structure comprising bulk-insulating TI BiSbTeSe2 (BSTS) sandwiched between a two-dimensional van der Waals ferromagnetic insulator Cr2Ge2Te6 (CGT) grown using Bridgeman method. The structure was assembled in the inert-gas glovebox to prevent oxidation and contamination of the interface. h-BN capping was used to protect CGT against degradation in air. The out-of-plane magnetization of CGT down to thicknesses of 18 nm was confirmed by exfoliating it directly atop our custom-designed Hall microsensor chips. The enhancement of proximal magnetism obtained by (1) the optimal thickness of BSTS, (2) using pressure to obtain a better interfacial coupling, and (3) by electrostatic gating to the Dirac gap will be discussed. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E03.00004: Nodal Arc in Disordered Dirac Fermions: Connection to Non-Hermitian Band Theory Michal Papaj, Hiroki Isobe, Liang Fu We show that Dirac fermion systems in two dimensions generally exhibit disorder-induced nodal arc replacing the nodal point and tilted Dirac cone, provided that the two components of the Dirac fermion correspond to two distinct orbitals unrelated by symmetry. This result is explicitly demonstrated using renormalization group analysis in a disordered Dirac model that we introduce, where the disorder potential acts differently on the two orbitals. As we show by numerical simulations and self-consistent Born approximation calculation, this drives the system into a new strongly disordered phase. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E03.00005: Interacting Dirac Semimetals Rui-Xing Zhang, Sheng-Jie Huang, Jiabin Yu The experimental discovery of three dimensional (3d) Dirac semimetals has opened up a new world of symmetry protected gapless state with non-trivial topological properties. While most existing studies have focused on the free fermion descriptions, we will show that interaction effects will significantly change the topological classification of Dirac semimetals. With the help of the dimensional reduction technique, we explicitly show that 3d Dirac semimetals protected by C_n rotation symmetries, such as Cd3As2 and Na3Bi, can be adiabatically connected to a gapped 3d axion insulator and gapless 1d axion strings in a symmetric way. This construction demonstrates that the anomaly nature of 3d Dirac semimetals is one dimensional. We further show that the non-interacting classification of a 3d Dirac semimetal generally reduces from Z to its Z_n subgroup in the presence of strong interactions. Our work lays the theoretical foundation for strongly interacting topological semimetals and paves the way for their future material realizations. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E03.00006: Influence of Landau levels in the phonon dispersion of Weyl semimetals Pierre Rinkel, Pedro Lopes, Ion Garate Discovered in high-energy physics, the chiral anomaly has recently made way to materials science by virtue of Weyl semimetals (WSM). Thus far, the main efforts to probe the chiral anomaly in WSM have concentrated on electronic phenomena. Nevertheless, recent theoretical works [1,2] have studied signatures of the chiral anomaly in the dynamics of lattice vibrations, to first order in the external magnetic field. In this work, we generalize those earlier results to magnetic fields of arbitrary strength by incorporating the influence of Landau levels in the phonon spectra. We predict a hybridization between plasmons and optical phonons that becomes potentially observable at high magnetic fields, and we identify fingerprints of chiral Landau levels in the sound velocity. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E03.00007: Anomalous off-diagonal thermal response in Mn$_{3}$Ge Liangcai Xu, Xiaokang Li, xiufang lu, Clement Collignon, Alaska Subedi, Benoit Fauque, Zengwei Zhu, Kamran Behnia We present a study of anomalous transverse response in non-collinear antiferromagnet Mn$_{3}$Ge down to sub-Kelvin temperature. Special attention is paid to the amplitude and temperature dependence of the anomalous Lorenz ratio $L^{A}_{ij}=\kappa^{A}_{ij}/T\sigma^{A}_{ij}$ relative to the Sommerfeld value. The contrast with Mn$_{3}$Sn [1] provides crucial information in the ongoing effort to identify the k-space location of the Weyl points. We also present measurements of the anomalous Ettingshausen and the anomalous Nernst effects in order to verify the Bridgman relation, a consequence of Onsager reciprocity. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E03.00008: Localized Plasmons in One Dimensional Topological Systems Zhihao Jiang, Roelof E Groenewald, Malte Roesner, Stephan Wolfgang Haas One dimensional topological systems (the Schrieffer-Su-Hegger model and the generalized Aubry-André-Harper model) support strongly localized electronic states in the topologically nontrivial phases. In this work, we study plasmon modes in these systems by calculating the real space dielectric function within the random phase approximation. We observe localized plasmon modes in the electron energy loss spectra. In the topologically nontrivial sectors, these localized plasmon modes are shown to originate from the localized electronic edge states by separating the full polarization into contributions from pure bulk transitions without localized electronic states and edge-bulk transitions involving localized electronic states. We also show that the Coulomb interaction plays a role of delocalizing plasmons due to its long-range property. Therefore, the localization of plasmon modes is less strong than the localized electronic states obtained from non-interacting tight binding models. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E03.00009: μ-ARPES studies of few-layer WTe2 Antonio Rossi, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Seng Huat Lee, Ronald Dean Redwing, Kevin Dressler, Inna Vishik WTe2 exhibits a wide variety of physics in its bulk and monolayer regimes including two different topological phases, non-saturating magnetoresistance, and superconductivity under pressure or gating. We will present micro-ARPES studies on bulk and few-layer WTe2, which connect microscopic electronic structure to observations from transport experiments. Doping-dependence, spatial inhomogeneity, and layer-dependence of electronic structure and interactions will be discussed. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E03.00010: "Glide-resolved selection rules for scanning-tunneling microscopy; application to Black Phosphorus and Zirconium(III) Chloride" Jung Pyo Hong, Benjamin Wieder, Zhijun Wang, Michael Zaletel, Andrei B Bernevig Recently Queiroz et al. predicted that the Bloch bands of nonsymmorphic crystals can exhibit novel selection rules in their quasiparticle interference (QPI) pattern, characterized by a quasi-Brillouin Zone (BZ) periodicity of extinction patterns in the momentum transfer channel. Here, we focus on glide reflection symmetry-i.e. the combined operation of mirror reflection and in-plane half-integer lattice translation - to quantitatively realize `glide-resolved QPI (gQPI) selection rules' on 2D minimal tight-binding models respecting the symmetries of layer group pma2 (LG 24), considering the limits of both strong and negligible spin-orbit coupling (SOC). We numerically compute the lattice- and energy-resolved local density of states (LDOS) in the presence of a local impurity and demonstrate the existence of quasi-BZ periodicity in the momentum-space LDOS. We propose Zirconium(III) Chloride and Black Phosphorus, whose monolayers respect pma2, as material candidates for the observation of gQPI in the presence and absence of SOC, respectively. By utilizing Topological Quantum Chemistry and density functional theory to construct tight-binding models, we find numerical evidence for gQPI in these materials, which can potentially be detectable through scanning-tunneling microscopy (STM). |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E03.00011: Purely Rotational Symmetry-Protected Topological Crystalline Insulator α-Bi4Br4 Chuang-Han Hsu, Tay-Rong Chang, XIAOTING ZHOU, Qiong Ma, Nuh Gedik, Arun Bansil, Vitor Pereira, Liang Fu, Suyang Xu, Hsin Lin Recent theoretical advances have proposed a new class of topological crystalline insulator (TCI) phases protected by rotational symmetries. Distinct from topological insulators (TIs), rotational symmetry-protected TCIs are expected to show unique topologically protected boundary modes: First, the surface normal to the rotational axis features ``unpinned'' Dirac surface states whose Dirac points are located at generic k points. Second, due to the ``higher-order'' bulk boundary correspondence, a 3D TCI also supports 1D helical edge states. Despite the unique topological electronic properties, to date, purely rotational symmetry-protected TCIs remain elusive in real materials. Using first-principles band calculations and theoretical modeling, we identify the van der Waals material α-Bi4Br4 as a TCI purely protected by rotation symmetry. We show that the α-Bi4Br4's (010) surface exhibits a pair of unpinned topological Dirac fermions protected by the two-fold rotational axis. These unpinned Dirac fermions show an exotic spin texture highly favorable for spin transport and a band structure consisting of van Hove singularities due to Lifshitz transition. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E03.00012: Modeling Image Potential States on Topological Semimetal Antimony Surface Haimei Zhang, Jianfeng Ge, Yang He, Yau Chuen Yam, Pengcheng Chen, Jennifer Hoffman Topological materials host protected surface states with locked spin and momentum degrees of freedom that are predicted to give rise to exotic excitations such as Majorana fermions and magnetic monopoles. The topological semimetal antimony (Sb) offers a pristine platform in which to search for these excitations. Here we present scanning tunneling spectroscopy (STS) studies of Sb at high energy where quantized image potential states form due to the binding between the tunneling electron and the polarized surface. We fit the energies of these quantized states using a one-dimensional model based on the image potential on metal surfaces, the electric field applied between tip and sample, and the work functions of both tip and sample materials. The model fits well with the experimental data as a function of tip-sample voltage and distance. The study of these image potential states allows exploration of the image charge geometry necessary to realize a magnetic monopole. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E03.00013: Pnictide square net materials with reduced symmetry, the rare earth diantimonides: electronic structure and topology Matteo Michiardi, Fabian Arnold, Elia Razzoli, Karl F. Fisher, Vaitheeswaran Ganapathy, Giorgio Levy, Fabio Boschini, Ilya Elfimov, Bo B Iversen, Philip Hofmann, Andrea Damascelli With the discovery of Dirac fermions, much research effort has been put into finding the structural elements that can generate Dirac-like degeneracies in the electronic band structures [1]. It was discovered that some layered materials can host planar square nets of group IV-V elements within their lattice. Analogously to graphene, these square nets possess a 2-atom basis and feature wide Dirac bands. Most of the known layered compounds that retain the electronic properties of the net, such as (Sr,Ca)MnBi2 and ZrSiS, crystallize in a tetragonal structure, and exhibit a Dirac semimetal or nodal line phase that can host a rich plethora of electronic and magnetic quantum properties [2]. In this talk we will show a new variety of square net semimetals whose structure breaks the 4-fold symmetry, the rare earth di-antimonides. These materials crystallize in the orthorhombic group Cmca reducing the overall symmetry of the system. We employed ARPES and DFT calculations on the series precursor, LaSb2, to study its electronic structure. We will discuss the effect that the symmetry reduction has on the electronic properties, on the Dirac states, as well as its interplay with spin-orbit coupling. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E03.00014: de Haas-van Alphen effect of correlated Dirac states in kagome metal Fe3Sn2 Linda Ye, Mun Keat Chan, Ross McDonald, David E Graf, Min Gu Kang, Junwei Liu, Takehito Suzuki, Riccardo Comin, Liang Fu, Joseph Checkelsky We report the study of the de Haas-van Alphen effect in the ferromagnetic kagome metal Fe3Sn2, where massive Dirac electronic states have been identified by spectroscopic means [1,2]. Through magneto-quantum oscillations we observe two quasi-2D Fermi surfaces that are consistent with the quasi-2D double Dirac cone structures. Moreover, these Fermi surfaces appear to change following the rotation of the soft ferromagnetic moment, implying a strong coupling of the Dirac states with the ferromagnetic order through spin-orbit coupling. Finally, these observations establish the bulk nature of the Dirac bands and offer unique insight into lattice-borne topological electronic states. These results are summarized in arxiv/1809.11159 [3]. |
Tuesday, March 5, 2019 10:48AM - 11:00AM |
E03.00015: Topological insulator materials for advanced nonlinear in-chip plasmonic devices Yinxiao Xiang, Chenhui Yan, Lian Li, Cheng Cen Topological insulator (TIs) has fascinating nonlinear optical properties that are inaccessible in classical materials. We report extraordinarily large third harmonic generation (THG) signal from telecom wavelength incidences in Bi2Se3 and Sb2Te3 grown by molecular beam epitaxy (MBE). Nonlinear optical measurements performed in samples with different thicknesses and stoichiometries are combined with angle-resolved photoemission spectroscopy (ARPES) characterizations to elucidate the nature of the giant THG signals. Moreover, by integrating with nanoscaled plasmonic devices on top of TIs, the strong plasmonic field enhancement further enables us to produce controllable nonlinear optical functionalities with very low input energy threshold. Our findings demonstrate a great potential for a new class of topological materials based on-chip nonlinear photonic devices. |
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